JP2005184882A - Switching power supply circuit - Google Patents

Switching power supply circuit Download PDF

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Publication number
JP2005184882A
JP2005184882A JP2003417780A JP2003417780A JP2005184882A JP 2005184882 A JP2005184882 A JP 2005184882A JP 2003417780 A JP2003417780 A JP 2003417780A JP 2003417780 A JP2003417780 A JP 2003417780A JP 2005184882 A JP2005184882 A JP 2005184882A
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Prior art keywords
switching
slope correction
input voltage
correction signal
power supply
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Pending
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JP2003417780A
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Japanese (ja)
Inventor
Hisazumi Watanabe
久純 渡邉
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Matsushita Electric Ind Co Ltd
松下電器産業株式会社
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Priority to JP2003417780A priority Critical patent/JP2005184882A/en
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Abstract

The present invention relates to a switching power supply circuit having a function of detecting an electric current flowing through a switching element 3 every ON period Ton of a switching pulse signal Vout and performing an overcurrent protection, and when adding a slope correction signal to the overcurrent detection signal. The problem is that the value of the amplitude of the slope correction signal varies depending on the input voltage Vi, and the value of the output current at which overcurrent limiting starts depends on the input voltage Vi.
A slope correction is made by superimposing a ramp waveform that is increased in proportion to an on period Ton of the switching pulse signal Vout on a rectangular wave that is synchronized with the switching pulse signal Vout output from the PWM control IC 9. When the input voltage Vi increases, the amplitude of the rectangular wave component increases and the ramp waveform component decreases, so that a constant slope correction signal can be added to the overcurrent detection signal regardless of the input voltage Vi. .
[Selection] Figure 1

Description

  The present invention relates to a sub-harmonic oscillation in a switching power supply circuit having a function of detecting a switching current flowing through a switching element every ON period Ton of a switching pulse signal Vout and performing an overcurrent limit based on the detected switching current detection signal. As a countermeasure, when the slope correction signal is superimposed on the switching current detection signal, it is improved that the amplitude value of the slope correction signal varies depending on the input voltage Vi in a switching power supply circuit having a wide input voltage range. This is a technique for making the amplitude of the slope correction signal constant regardless.

  The switching power supply circuit has various protection functions in preparation for abnormal situations such as overcurrent and overvoltage.

  FIG. 7 shows a switching power source in which the switching current detection unit 6 detects a switching current flowing through the switching element 3 every ON period Ton of the switching pulse signal Vout, and the PWM control IC 9 limits the circuit operation based on the switching current detection signal. It is an example of the block diagram which shows the structure of the power supply device of a circuit.

  In FIG. 7, the input voltage Vi is applied to the input and the switching element 3 provided on the primary side is turned on / off to transmit power to the secondary side via the transformer. On the secondary side, the rectifying diode 4 Is rectified and smoothed by the output smoothing unit 5 to produce a stabilized output voltage Vo.

  The output voltage signal detected by the output voltage detection unit 7 is applied to the output voltage control sensing terminal Fb of the PWM control IC 9 via the primary / secondary signal transmission unit 8 using a photocoupler or the like, and PWM control is performed. The IC 9 outputs a switching pulse signal Vout that makes the output voltage Vo constant.

  Further, the switching current detection unit 6 using a current transformer or the like detects the switching current flowing through the switching element 3 every ON period Ton of the switching pulse signal Vout, and the detected switching current detection signal is detected by the PWM control IC 9. Applied to the switching current detection terminal CLM.

  The overcurrent operation in this configuration will be described below.

  When the switching current detection signal applied to the switching current detection terminal CLM of the PWM control IC 9 exceeds the threshold value determined by the PWM control IC 9, the PWM control IC 9 further switches the switching element during the same switching period Ts. 3, the on period Ton of the switching pulse signal Vout is limited so that no current flows in the circuit.

  In the next switching cycle, the PWM control IC 9 outputs the switching pulse signal Vout as usual, and the switching current detection signal applied to the switching current detection terminal CLM of the PWM control IC 9 is determined by the PWM control IC 9 again. When the threshold value is exceeded, during the same switching period Ts, the PWM control IC 9 repeats the operation of limiting the ON period Ton of the switching pulse signal Vout so that no more current flows through the switching element 3.

  However, in this circuit configuration, if the voltage at the switching current detection terminal CLM fluctuates slightly due to disturbance or the like, a time lag occurs when the PWM control IC 9 detects the overcurrent and stops the output of the switching pulse signal Vout. Since the ON period Ton of the switching pulse signal Vout varies compared to when it is normally detected, if the duty ratio exceeds 50%, the ON period Ton of the switching pulse signal Vout increases and converges every time switching is performed. In some cases, low-frequency oscillation called subharmonic oscillation occurs, or even if the operation is performed with a duty ratio of 50% or less, even if low-frequency oscillation is not reached, unstable operation may occur.

  As a countermeasure against this low-frequency oscillation and unstable operation, FIG. 7 shows that the slope correction signal waveform generator 10 increases in proportion to the ON period Ton of the switching pulse signal Vout output by the PWM control IC 9 as shown in FIG. A slope correction signal is applied to the switching current detection terminal CLM.

  In this method, the switching current detection signal and the slope correction signal are applied to the switching current detection terminal CLM of the PWM control IC 9 so that the signal at the switching current detection terminal CLM has a large slope as shown in FIG. It becomes difficult to receive.

  Here, for example, when the switching current detection terminal CLM of the PWM control IC 9 detects negative voltage, the configuration of the slope correction signal waveform generation unit 10 includes a circuit as shown in FIG.

  However, as shown in FIG. 9, the amplitude of such a slope correction signal increases in proportion to the on period Ton of the switching pulse signal Vout output from the PWM control IC 9, and thus varies depending on the input voltage Vi. When the input voltage Vi is high, the amount of correction changes depending on the on period Ton, and the on period Ton becomes shorter and the amplitude of the slope correction signal becomes smaller. When the input voltage Vi is small, the on period Ton becomes longer and the slope correction is performed. The signal amplitude also increases.

  As a result, as shown in FIG. 11, when the input voltage Vi is high, the value of the output current that starts limiting the overcurrent is larger than when the input voltage Vi is small.

  Thus, since the value of the output current which starts overcurrent limitation will become large if the input voltage Vi becomes high, the semiconductor element etc. had the subject that the element of a bigger rating was needed.

For example, Patent Document 1 and Patent Document 2 are known as prior art document information relating to the invention of this application.
JP-A-6-217533 Japanese Patent Laid-Open No. 11-41924

  The present invention solves the above-described conventional problems, and starts limiting the overcurrent by applying a slope correction signal having a constant amplitude to the switching current detection terminal CLM of the PWM control IC 9 without depending on the input voltage Vi. The purpose is to keep the output current constant.

  In order to achieve the above object, the present invention has the following configuration.

  According to the first aspect of the present invention, the switching pulse signal output from the PWM control IC 9 as shown in FIG. 2 is used instead of the slope correction signal of FIG. 9 applied to the conventional switching current detection terminal CLM. A slope correction signal in which a ramp waveform that increases in proportion to the on period of the switching pulse signal Vout is superimposed on a rectangular wave whose amplitude increases as the input voltage Vi increases in synchronization with Vout is applied. .

  At this time, the slope correction signal cancels each other so that the rectangular wave component increases as the input voltage Vi increases, while the ramp waveform component decreases. As shown in FIG. A substantially constant characteristic with respect to the voltage can be obtained, the value of the output current for starting overcurrent limitation can be made constant regardless of the input voltage Vi, and at the same time, the signal applied to the switching current detection terminal CLM is As shown in FIG. 3, the slope correction signal is superimposed on the switching current detection signal, and the slope is increased similarly to the signal to the switching current detection terminal CLM to which the conventional slope correction signal is applied, and the sub-harmonic oscillation As a countermeasure against unstable operation, it has the same effect as the conventional one.

  In the conventional method, the amplitude of the slope correction signal is affected by the input voltage Vi. However, in the present invention, the amplitude of the slope correction signal is substantially constant with respect to each input voltage. Therefore, as shown in FIG. Since the value of the output current for starting the overcurrent limitation due to can be made almost constant, the circuit can be protected from the overcurrent without applying excessive thermal stress to each semiconductor element or the like.

  Further, by changing the amplitude of the rectangular wave component of the slope correction signal, it is possible to arbitrarily adjust the value of the output current that starts overcurrent limitation by the input voltage Vi.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a specific configuration example for generating a slope correction signal of the overcurrent limiting device of the switching power supply circuit according to the first embodiment.

  1 corresponds to the slope correction signal waveform generation unit 10 in the block diagram showing the configuration of the conventional switching power supply circuit of FIG. 7. In the present invention, the configuration other than the slope correction signal waveform generation unit 10 is the block diagram of FIG. 7 is also used in the following description of the present invention.

  Here, a case where the switching current detection terminal CLM in the PWM control IC 9 is negatively detected is taken as an example. However, even if the switching current detection terminal CLM is positively detected, the same can be considered. In this configuration example, the switching element 3 is connected in series. For example, a method of detecting a voltage drop at the switching element 3 is also conceivable.

  7 shows an example of an insulated forward circuit, but the slope correction of the overcurrent limiting device for the switching power supply circuit according to the present invention can be performed in any configuration such as a flyback system or a non-insulated circuit. The signal can be applied.

  In the ramp waveform generating unit including resistors R1, R2, R5, a capacitor C1, and a transistor Q1 in FIG. 1, the switching pulse signal Vout output from the PWM control IC 9, the DC voltage Vc for supplying power to the PWM control IC 9, etc. The transistor Q1 is turned on during the off period of the output pulse voltage Vout using the transistor Q1 to charge the voltage of the capacitor C1 to the DC voltage Vc for supplying power to the PWM control IC 9, and the on period Ton of the output pulse voltage Vout. Further, by discharging the electric charge of the capacitor C1 by the resistors R2 and R6, the ramp waveform (shaded portion in the figure) of the slope correction signal shown in FIG. 2 is created.

  At this time, the time constant composed of the capacitor C1 and the resistor R2 + R5 is set to a sufficiently large value with respect to the on period Ton of the switching pulse signal Vout, and the discharge curve has a slope that is nearly linear in the on period Ton of the switching pulse signal Vout. ing.

  As a method of creating the ramp waveform, any method such as using a triangular wave oscillation signal of the PWM control IC 9 may be used.

  In the rectangular wave generator composed of the resistors R6 to R11, the transistors Q4 to Q6, the diode D1, and the Zener diode ZD1, the voltage obtained by subtracting the voltage across the Zener diode ZD1 from the input voltage Vin while the switching pulse signal Vout is off Applied to the resistor R5 via Q5, the resistor R6, and the diode D1, a rectangular wave component proportional to the input voltage Vi of the slope correction signal shown in FIG. 2 is generated.

  In FIG. 1, a Zener diode ZD1 determines an input voltage Vin for starting input voltage correction using this rectangular wave component.

  Note that any method other than the above method may be used to generate the rectangular wave component, and a method of directly applying the input voltage Vi by resistance division without using a Zener diode is also conceivable.

  Transistors Q2 and Q3 and resistors R3 and R4 are drive circuits for applying a signal to the switching current detection terminal CLM.

  5 and 6 show waveforms at points c and d in FIG. 1, respectively.

  As shown in FIG. 5, the voltage at point c in FIG. 1 is a positive voltage, and the level must be shifted to minus in order to apply it to the PWM control IC for detecting minus.

  Capacitor C2 is for level shifting.

  The level shift may be shifted to the minus side by any method.

  As described above, since the slope correction signal applied to the switching current detection terminal CLM can be made constant regardless of the input voltage Vi, the value of the output current that starts limiting the overcurrent regardless of the input voltage Vi is shown in FIG. 4 can be constant.

  For this reason, the circuit can be protected from an overcurrent without applying excessive thermal stress to each semiconductor element.

  The slope correction signal of the overcurrent limiting device of the switching power supply circuit according to the present invention has a constant amplitude regardless of the input voltage Vi, and the fluctuation of the value of the output current that starts overcurrent limiting by the input voltage Vi is detected. Therefore, it is useful in a switching power supply circuit having a wide input voltage range.

Slope correction signal generation circuit configuration diagram showing an embodiment of the present invention Waveform diagram for explaining the slope correction signal applied to the switching current detection terminal CLM in the present invention The wave form diagram for demonstrating the signal applied to the switching current detection terminal CLM when the slope correction signal in this invention is superimposed The characteristic view which shows the change by the input voltage Vi of the value of the output current which starts the restriction | limiting of an overcurrent when the slope correction signal in this invention is superimposed Waveform diagram of point c in the embodiment shown in FIG. Waveform diagram of point d in the embodiment shown in FIG. 1 of the present invention The block diagram which shows the structure of the switching power supply circuit which has the function to detect the electric current which flows through the switching element 3 for every ON period Ton of the switching pulse signal Vout, and to perform an overcurrent protection Conventional slope correction signal generator circuit configuration diagram Waveform diagram for explaining a slope correction signal applied to a conventional switching current detection terminal CLM Waveform diagram for explaining a signal applied to switching current detection terminal CLM when a conventional slope correction signal is superimposed The characteristic view which shows the change by the input voltage Vi of the value of the output current which starts the restriction | limiting of an overcurrent when the conventional slope correction signal is superimposed

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input filter part 2 Transformer 3 Switching element 4 Rectifying diode 5 Output smoothing part 6 Switching current detection part 7 Output voltage detection part 8 Primary-secondary signal transmission part 9 PWM control IC
10 Slope Correction Signal Waveform Generation Unit Vi Switching Power Supply Circuit Input Voltage Vo Switching Power Supply Circuit Output Voltage CLM Switching Current Detection Terminal of PWM Control IC 9 Vout Switching Pulse Signal Output from PWM Control IC 9 Vc Power Supply to PWM Control IC 9 DC voltage Fb Output voltage control sensing terminals of PWM control IC 9 R1-R12 Resistors Q1-Q6 Transistors C1, C2 Capacitors ZD1 Zener diode D1 Diode GND Ground Ts Switching period of switching pulse signal Vout Ton Switching pulse signal Vout ON period

Claims (3)

  1. A switching power supply circuit that converts an input voltage into a stable DC voltage, a switching current detection unit that detects a current flowing through a switching element every ON period of a switching pulse signal, and an output voltage that detects an output voltage of the switching power supply circuit Overcurrent limiting is performed based on a detection unit and a switching current detection signal detected by the switching current detection unit, and output voltage control is performed based on an output voltage detection signal detected by the output voltage detection unit And a slope correction signal waveform generator for superimposing a slope correction signal on the switching current detection signal, and the slope correction signal is a rectangular wave synchronized with the switching pulse signal output by the control unit. The ramp waveform that increases in proportion to the ON period of the switching pulse signal. Switching power supply circuit, which is a superimposed slope correction signal.
  2. 2. The switching power supply circuit according to claim 1, wherein an amplitude of a rectangular wave component of the slope correction signal increases as an input voltage of the switching power supply circuit increases.
  3. 2. The switching power supply circuit according to claim 1, wherein the rectangular wave of the slope correction signal has a function of starting superposition according to a threshold value of an input voltage.
JP2003417780A 2003-12-16 2003-12-16 Switching power supply circuit Pending JP2005184882A (en)

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008161001A (en) * 2006-12-26 2008-07-10 Ricoh Co Ltd Current-mode control type switching regulator and operation control method therefor
JP2009232578A (en) * 2008-03-24 2009-10-08 Seiko Epson Corp Control circuit provided in switching power supply circuit
CN101820221A (en) * 2009-08-14 2010-09-01 崇贸科技股份有限公司 Switch adjuster
US7986537B2 (en) 2007-10-22 2011-07-26 Sanken Electric Co., Ltd. Overcurrent-protected switching-mode power supply
JP2011217476A (en) * 2010-03-31 2011-10-27 Fujitsu Semiconductor Ltd Power supply device, control circuit, and control method of power supply device
JP2013258789A (en) * 2012-06-11 2013-12-26 Diamond Electric Mfg Co Ltd Step-down dc/dc converter
US9036383B2 (en) 2012-09-19 2015-05-19 Fuji Electric Co., Ltd. Power supply device control circuit
US9240727B2 (en) 2011-07-12 2016-01-19 Fuji Electric Co., Ltd. Switching power supply device control circuit having an overcurrent protection control circuit

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008161001A (en) * 2006-12-26 2008-07-10 Ricoh Co Ltd Current-mode control type switching regulator and operation control method therefor
US7986537B2 (en) 2007-10-22 2011-07-26 Sanken Electric Co., Ltd. Overcurrent-protected switching-mode power supply
JP2009232578A (en) * 2008-03-24 2009-10-08 Seiko Epson Corp Control circuit provided in switching power supply circuit
CN101820221A (en) * 2009-08-14 2010-09-01 崇贸科技股份有限公司 Switch adjuster
TWI396365B (en) * 2009-08-14 2013-05-11 System General Corp Switching regulators
JP2011217476A (en) * 2010-03-31 2011-10-27 Fujitsu Semiconductor Ltd Power supply device, control circuit, and control method of power supply device
US9240727B2 (en) 2011-07-12 2016-01-19 Fuji Electric Co., Ltd. Switching power supply device control circuit having an overcurrent protection control circuit
JP2013258789A (en) * 2012-06-11 2013-12-26 Diamond Electric Mfg Co Ltd Step-down dc/dc converter
US9036383B2 (en) 2012-09-19 2015-05-19 Fuji Electric Co., Ltd. Power supply device control circuit

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